Human joint surfaces are covered by articular cartilage that provides a resilient, durable surface with low friction. Cartilage is an avascular tissue that has a small number of chondrocytes encapsulated within an extensive extracellular matrix. The cartilage acts to distribute mechanical forces and to protect subchondral bone. The knee is a particular instance of a cartilage surfaced (the condyle) bone area. The knee comprises three bones—the femur, tibia, and patella that are held in place by various ligaments. Corresponding chondral areas of the femur and the tibia form a hinge joint and the patella acts to protect the joint. Portions of the chondral areas as well as the undersurface of the patella are covered with articular cartilage that allows the femur, patella and tibia to smoothly glide against each other without causing damage.
Damage to the articular cartilage, subchondral bone or both can result from traumatic injury or a disease state. For example, articular cartilage in the knee can be damaged due to traumatic injury as with athletes and via a degenerative process as with older patients. The knee cartilage does not heal well due to the lack of vascularity. Hyaline cartilage in particular has a limited capacity for repair and lesions in this material, without intervention, can form scar tissue lacking the biomechanical properties of normal cartilage.
A number of procedures are used to treat damaged articular cartilage. Currently, the most widely used procedure involves lavage, arthroscopic debridement and repair stimulation. Repair stimulation is conducted by several methods including, drilling, abrasion arthroplasty and microfracture. The goal of these procedures is to penetrate into subchondral bone to induce bleeding and fibrin clot formation. This reaction promotes initial repair. However, the resulting formed tissue is often fibrous in nature and lacks the durability of normal articular cartilage.
Another known treatment involves the removal and replacement of the damaged articular cartilage with a prosthetic device. However, historically, artificial prostheses have largely had limited success since they are non-elastic, and therefore lack the shock-absorbing, properties characteristic of the normal cartilage. Moreover, the known artificial devices have shown a reduced ability to withstand the high and complex forces inherent to routine knee joint function.
In an attempt to overcome the problems associated with the above techniques, osteochondral transplantation, also known as “mosaicplasty” or “OATS” has been used to repair articular cartilage. This procedure involves removing injured tissue from the articular defect and drilling cylindrical openings in the area of the defect and underlying bone. Cylindrical plugs, consisting of healthy cartilage overlying subchondral bone, are harvested from another area of the patient, typically from a lower weight-bearing region of the joint under repair, or from a donor patient, and are implanted in the host openings. However, in these cases, if the opening is too large, the graft can rotate or move within the host site and become loose, which will prevent bio-integration with the surrounding tissues. Further, if the host site is too small, significant tissue and cellular damage can occur to the graft during the implantation.
Historically, osteochondral grafting has been used successfully to repair chondral damage and to replace damaged articular cartilage and subchondral bone. First, in this procedure, cartilage and bone tissue of a defect site are removed by routing to create a cylindrical bore of a precise geometry. Then a cartilage and subchondral bone plug graft is harvested in a matching geometry. The donor plug graft is typically removed from another body region of less strain. The donor plug graft can be harvested from a recipient source (autograft) or from another suitable human or other animal donor (allograft). The harvested plug graft is then implanted into the bore of the routed defect site. Healing of the plug graft to the host bone results in fixation of the plug graft to the surrounding host region.
Success of the grafting process is dependant on the intimate seating and sizing of the graft within the socket. First, surface characteristics of the plug graft are critical. For the procedure to be successful, the surface of the transplanted plug graft must have the same contour as the excised osteochondral tissue. If the contour is not a correct match, a repaired articular surface is at risk for further damage during motion. Additionally, some graft shapes do not pack well into irregular defects. The graft may have a propensity to rotate resulting in poor integration of the graft to the surrounding host tissue. An improperly placed and sized plug graft can result in host tissue integration failure and post implantation motion.
Since the plug graft is press-fit within a host site, accurate sizing of the plug graft is critical to the success of the implanted graft material. Hence, a surgeon must accurately cut and trim the plug graft to size in order to ensure a proper press fit within the recipient host site. If the plug graft is too small or too large or otherwise incorrectly sized, the plug graft may be damaged upon implantation or damage the host site when inserted. Extraction procedures and tools can cause further damage to the boundary host site cells and to the graft structural integrity.
Thus, there is a need for a multi-functioning “back table” cutting instrument in which a donor plug graft may be secured and that allows for accurate length cutting and cross-sectional trimming without causing damage to the donor plug graft prior to implantation.